Aeration and flotation cell and method of froth flotation



J. F. MYERS May 21, 1957 AERATION AND FLOTATION CELL AND METHOD OF FROTH FLOTATION Filed April 6, 1955 INVEN'ibR John F. Myers MMYW I ATTORNEYIS AERATION AND FLOTATION CELL AND METHOD OF FROTH FLOTATION John F. Myers, Greenwich, Conn., assignor, by mesne assignments, to Mining Process and Patent Company, Denver, (3010., a corporation of Delaware Application April 6, 1953, Serial No. 346,989 6 Claims. (Cl. 209166) This invention relates to cells for aeration and to a method of froth flotation of finely divided materials. More particularly this invention relates to such cells of the double runner or double impeller type.

Heretofore various types of double runner or impeller type flotation cells have been proposed in which a vertical shaft rotates two impellers in a cell or vessel with the smaller impeller adjacent the bottom of the vessel and the larger impeller adjacent the pulp level in the cell. The lower impeller actsto mix the material to be concentrated with water to form a pulp which should include suitable flotation reagents and to pass the pulp upwardly rom the bottom of the cell toward the upper impeller. The upper impeller draws air downwardly through a hood arranged over it and aerates the pulp drawn from the bottom of the cell by the lower impeller. A froth containing the desired material or product to be removed from the pulp is formed on the surface of the pulp in the cell and flows off in conventional manner.

These prior art devices have proved to be faulty in various ways. Since the impellers are working in a pulp of a water and comminuted solids mixture wear of all parts is rapid and excessive power is required to rotate the impellers. Because of this fact deep cells cannot be used in prior art structures because the power demands increase rapidly with depth.

Prior art cells also banked rapidly, that is, a product of flotation separation accumulated in the corners and bottom of the cell thus reducing the volume of the cell and its ultimate efficiency.

In these prior art cells the lower impeller fed the pulp upwardly to the upper impeller which in turn aerated the pulp by forming a froth floating above the water level. Efficiency of this action was impaired by the upper impeller throwing particles outwardly which tended to break the froth with consequent reduction in efficiency of operation.

In these prior art structures the distance between the upper impeller and the top of the hood surrounding the same to furnish an air conduit was critical and unless the adjustment was accurate aeration was not cfiicient.

The present invention provides a novel flotation cell, utilizing the method of forming a vortex beneath the upper impeller which passes downwardly through the lower impeller to overcome most of the difliculties heretofore experienced in prior art cells. To establish this vortex the lower impeller is so arranged that instead of circulating pulp upwardly it circulates pulp downwardly toward the bottom of the cell then outwardly and upwardly toward the surface of the pulp in the cell and toward the upper impeller. Under these circumstances both impellers may be rotated at reduced velocities with a resulting decrease in wear of parts and lower power consumption. The vortex provides intimate mixing with proper aeration and utilizes the entire capacity of the cell for this purpose. The circulation of the pulp downwardly, outwardly and upwardly in the cell prevents banking so that the efiiciency of the cell is greatly enhanced.

" nited States Patent 9 ice It is accordingly an object of the present invention to provide a novel flotation cell of the double runner or impeller type in which a vortex is created beneath the upper impeller extending downwardly through the lower impeller to provide intimate mixing and proper aeration of the pulp throughout the entire volume of the cell.

Another object of the present invention is to provide a novel flotation cell in which the downwardly and outwardly directed currents of air and pulp prevent banking in the lower corners of the cell with a resulting increased capacity of the cell.

Another object is to provide such a cell in which the rising aerating bubbles rise from adjacent the bottom of the cell to provide ample time for collecting material concentrated in the froth.

Another object is to provide such a cell which has increased depth with a resulting increase in volume of pulp in the cell without excessive power consumption.

Another object is to provide such a cell in which both impellers act to aerate the pulp.

Another object is to provide such a cell in. which the long path of the aerating bubbles through the pulp enables micron 'sized particles of material to be concentrated in the froth to be picked up in the froth and thus separated from the body of the pulp.

Another object is to provide such a cell in which the comminuted particles are not concentrated adjacent the runner thus requiring maximum available power during aeration but are distributed throughout the volume of the cell for complete aeration.

Another object is to provide such a cell having increased efiiciency with lower power consumption and reduced wear of all parts, thereof.

Another and still further object is to provide a novel method of froth flotation in which an aerating mixing vortex is employed.

Other and further objects of the present invention will be apparent from the following description of an illustrative embodiment of the same.

The novel flotation cell of the present invention is capable of various mechanical embodiments for carrying out the novel method hereof, one of which is shown in the accompanying drawing and is described hereinafter for purposes of illustrating the invention. v Reference should therefore be had to appended claims to determine the scope of this invention.

In the accompanying drawing, in which like reference characters indicate like parts,

Fig. 1 is a vertical sectional view of an illustrative embodiment of the novel flotation cell of the present invention to show the relative positions of the several parts thereof and showing the vortex created beneath the upper runner and extending downwardly through the lower runner;

Fig. 2 is a cross sectional view on the line 22 of Fig. 1 to show the details of the upper impeller and its associated hood;

Fig. 3 is a cross section view on the line 3-3 of Fig. 1 to show the details of the lower impeller; and

Fig. 4 shows a plurality of the cells of Fig. 1 arranged in an open-topped trough without dividing partitions.

Referring now to the several figures, 10 is a suitable tank or cell having'appropriate dimensions and is provided with a lip 11 over which the aerated pulp or froth is permitted to flow. Cell 10 is provided with a suitable bottom 12 and a pair of beams 13 and 14 extend across the top of cell 10 and are suitably secured thereto.

A cylindrical sleeve 15 is suitably secured between beams 13 and 14 and is arranged so that its long axis lies in the center line of cell 10. Cylindrical sleeve 15 terminates in an outwardly extending flange 16 to which is secured a suitable hood 17 having a downwardly extending annular flange 18.

A vertical shaft 19 is mounted for rotation within sleeve 15 and its center line lies in the axis of sleeve 15 and in the center line of the cell 10. An upper runner or impeller 20 is secured to shaft 19 and rotates within the chamber provided by hood 17 and annular flange 18. Runner 20, as seen in Fig. 2, comprises a plurality of radially disposed blades 21 secured to or cast integrally with a lower solid plate 28 and when rotated by shaft 19 draws air downwardly through cylindrical sleeve 15 and forces the same downwardly and outwardly into the cell It around the flange 18 as indicated by the arrows.

Shaft 19 carries a lower runner or impeller 22 adjacent the bottom 12 of cell 10. Runner 22 has a multiplicity of blades here shown as four blades 23 which are so pitched with respect to their direction of rotation that they will draw pulp downwardly and discharge it toward the bottom 12 of cell 10. It is to be expressly understood that any convenient number of blades 23 may be used. Lower runner 22 is surrounded by a cylindrical shield 24 which is provided with a plurality of openings 25 at its bottom to allow circulation of pulp outwardly therethrough in the direction of the arrows in Fig. l.

The arrows 26 in Fig. 1 indicate a desirable pulp level in the cell.

In Fig. 4 a desired number of the units of Fig. 1, here shown for convenience as three but more or less than three may be used as necessary, are mounted in an opentopped trough 29 and are suitably spaced from each other. No partitions are used between the units. Trough 29 is provided with a discharge lip 11;

With the novel flotation cell of the present invention organized as above described and with the cell filled with pulp including suitable flotation reagents to the indicated level, when shaft 19 is rotated at suitable speeds upper runner 20 draws air downwardly through sleeve 15 and discharges it downwardly and outwardly beneath flange 18 in the directions of the arrows in Fig. l. A part of this air escapes laterally to create froth and the remainder passes beneath runner 20 and a vortex is created. Lower runner 22 is rotated at the same time and draws pulp and air downwardly within shield 24 and discharges mixed pulp and air outwardly through the openings 25. When both impellers 20 and 22 are rotating up to speed a vortex generally indicated at 27 is established beneath runner 2t and extends downwardly through impeller 22 as shown in Fig. 1. into cell 10 and intimately mixes the air with the pulp which is passing through runner 22 and then outwardly through openings 25. Thus air bubbles have the entire depth of cell 12 in which to pick up the particles to be separated in the froth and the flotation action of the cell is of increased efliciency.

Comparative tests were run with cells operated in ac cordance with the present invention and with a Booth cell of the type well known to the art. The Booth flotation cell has long been considered to be an eflicient flotation cell. The results of these tests are tabulated below and clearly establish the superiority of the flotation action of the present invention.

B th Myers Myers Cell Cell #1 Cell #2 1. Size of Machine #24 #24 #24 2. \Vidth 4'7 4'7 4'7 3- 58 /45 14% 4. ll. 54 11.54 11. 54 5. M 435 325 268 6. Horsepower For Cell 5.0 7 2. 9 7. H. PJFt. of Machine l 1.20 .89 .70 8. H. P./l00 Ftfi of Pulp 10. 40 7. 70 6. ()4

Bubble Air 9. 1*"tfl/h/Ii1r/Ft. Surface 2.16 2.05 1. l4 l0. Ftfi/MinJlOO FL Bulp 55.3 63. 7 35. 4 ll. Ft. /Min./E. P 5. 31 8.27 5. 86

This vortex draws air downwardly Lines 8 and 11 clearly show the advantages of the Myers cell as compared to the Booth cell.

Thus it will be seen that by rotating the lower impeller 22 in such a way that the pulp is drawn downwardly therethrough and discharged outwardly therefrom along the bottom 12 of cell 10 so that a vortex is established beneath the upper runner extending down through lower runner 22 the aerating action of the flotation cell of the present invention is enhanced and its efliciency is markedly increased over flotation cells of the prior art.

In the embodiment of Fig. 4 the efliciency of the individual units of Fig. l is enhanced by the arrangement there shown. No separating partitions are required between units and the pulp passes from unit to unit with a cumulative action in the formation of froth.

it should now be obvious to those skilled in the art that the present invention meets all of the objectives described above and has many advantages over flotation cells of the prior art.

Changes in or modifications to the above described illustrative embodiment of the present invention may now be suggested to those skilled in the art without departing from the present inventive concept and reference should therefore be had to the appended claims to determine the scope of this invention.

What is claimed is:

1. An aeration and flotation cell including a container for liquid, a drive shaft, means for rotating said drive shaft in a single direction of rotation, a hood about the upper portion of the shaft and an upper impeller mounted on the shaft beneath the hood to draw air therethrough, and means for creating a vortex beneath said upper impeller including means cooperating with said hood and with said upper impeller to discharge the air in a downward direction, a lower impeller mounted on the shaft adjacent the bottom of the container and blades on said lower impeller constructed and arranged to circulate pulp and reagents away from the upper impeller and downwardly toward and outwardly along the bottom of the container when said lower impeller is rotated with said upper impeller in the direction of rotation of said shaft, said vortex extending downwardly to said lower impeller to provide air to the lower impeller.

2. An aeration and flotation cell as described in claim 1 in which said lower impeller is surrounded by a cylindrical shield spaced therefrom and spaced from the bottom of the container, the vortex extending downwardly into said shield.

3. An aeration and flotation cell as described in claim 1 in which said means for discharging the air drawn through the hood in a downward direction include a downwardly extending portion or" said hood spaced from and surrounding the upper impeller.

4. An aeration and flotation cell including a container for a finely divided material mixed in a liquid, an impeller mounted for rotation in a single direction in the body of the liquid in the container and a hood over the impeller for channeling air thereto, a cylindrical shield spaced from the bottom of the container, means for creating a vortex beneath said impeller including means cooperating with said hood and with said upper impeller to discharge the air in a downward direction and a second impeller in said shield adapted to circulate liquid away from the first named impeller when rotated in the same direction as said first impeller and downwardly toward and outwardly along the bottom of the container, said vortex extending into said shield and to said second impeller.

5. An aeration and flotation cell as described in claim 4 in which said means for discharging the air in a downward direction include a portion of the hood extending laterally over the top of the first impeller and then downwardly in an annular portion spaced from the periphery thereof.

6. A method of froth flotation, the steps of drawing air into a body of liquid, discharging a portion of such air laterally in the body of the liquid and creating a vortex beneath the surface of the liquid extending from the region of lateral discharge of air in the liquid downwardly therein to adjacent the lower surface of the liquid with the remainder of such air.

References Cited in the file of this patent UNITED STATES PATENTS Daman Feb. 13, 1940 Ingalls Feb. 18, 1941 Booth Dec. 30, 1947 Daman Feb. 27, 1953 Daman Sept. 8, 1953 

1. AN AEARATION AND FLOATION CELL INCLUDING A CONTAINER FOR LIQUID, A DRIVE SHAFT, MEANS FOR ROTATING SAID DRIVE SHAFT IN A SINGLE DIRECTION OF ROTATION, A HOOD ABOUT THE UPPER PORTION OF THE SHAFT AND AN UPPER IMPLLER MOUNTED ON THE SHAFT BEANEATH THE HOOD TO DRAW AIR THERETHROUGH, AND MEANS FOR CREATING A VORTEX BEANEATH SAID UPPER IMPELLER INCLUDING MEANS COOPERATING WITH SAID HOOD AND WITH SAID UPPER IMPELLER TO DISCHARGE THE AIR IN A DOWNWARD DIRECTION, A LOWER IMPELLOOR MOUNTED ON THE SHAFT ADACENT THE BOTTOM OF THE CONTAINER AND BLADES ON SAID LOWER IMPELLOR CONSTRUCTED AND ARRANGED TO CIRCULATE PULP AND REAGENTS AWAY FROM THE UPPER IMPELLOOR AND DOWNWARDLY TOWARD AND OUTWARDLY ALONG THE BOTOM OF THE CONTAINER WHEN SAID LOWER IMPELLOR IS ROTATED WITH SAID UPPER IMPELLOR IN THE DIRECTION OF ROTATION OF SAID SHAFT, SAID VORTEX EXTENDING DOWNWARDLY TO SAID LOWER IMPELLOR TO PROVIDE AIR TO THE LOWER IMPELLER. 